1. Field of the Invention
The present invention relates to a negative active material for rechargeable lithium batteries, methods of preparing the same and rechargeable lithium batteries including the same.
2. Description of the Related Art
Rechargeable lithium batteries contain materials that are capable of reversibly intercalating or deintercalating lithium ions in positive and negative electrodes, and include an organic electrolyte solution or a polymer electrolyte between the positive and negative electrodes. Rechargeable lithium batteries generate electric energy by oxidation and reduction reactions of lithium ions at the positive and negative electrodes.
Composite metal oxides such as LiCoO2, LiMn2O4, LiNiO2, LiNi1-xCoxO2 (where, 0<x<1), LiMnO2, and so on have been researched for use as positive active materials.
Lithium metals have generally been used as a negative active material for the rechargeable lithium batteries. However, lithium metals can cause short circuits and pose potential threats of explosions due to the formation of dendrites. Therefore, carbonaceous materials such as amorphous carbons, crystalline carbons, etc., have recently been used as the negative active material in place of lithium metals. However, such carbonaceous materials can have irreversible capacity of 5 to 30% during the first several cycles, which wastes lithium ions, and prevents the active material from being fully charged and discharged. Therefore, carbonaceous negative active materials have poor energy densities.
While other metal negative active materials such as Si, Sn, and so on, are supposed to have high capacity, they have non-reversible capacity characteristics. Another material, such as tin oxide, has also been proposed as an alternative to the carbonaceous material negative active material. However, if the metal negative active material is included at 30% or less, the initial coulomb efficiency decreases. Further, as lithium ions are continuously intercalated and deintercalated to generate a lithium-metal alloy, the capacity further decreases and the capacity retention rate remarkably deteriorates after 150 charge and discharge cycles, thereby making it not commercially viable.